Polarization state monitoring device, polarization state monitoring method, and program

Abstract

To provide new technology for monitoring the polarization state of an optical reception signal.SOLUTION: A polarization state monitoring device identifies, for each of a plurality of first partial periods obtained from a monitoring period, a first polarization state vector representing the polarization state of an optical reception signal in the first partial period, and identifies, for each of a plurality of second partial periods obtained from the monitoring period, a second polarization state vector representing the polarization state of an optical reception signal in the second partial period. The polarization state monitoring device calculates the angle of rotation of the polarization state vector for each of a plurality of pairs of the first polarization state vectors and for each of a plurality of pairs of the second polarization state vectors. The polarization state monitoring device determines whether the length of the first partial period is appropriate on the basis of the angle of rotation of the first polarization state vector and the angle of rotation of the second polarization state vector, and when determining that the length of the first partial period is appropriate, outputs change speed data representing the speed of the change in the polarization state in the monitoring period.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a polarization state monitoring device, a polarization state monitoring method, and a program. [Background technology]

[0002] In optical communication systems, a technology for monitoring changes in the polarization state of an optical signal has been developed. For example, Non-Patent Document 1 discloses a technology for monitoring changes in the polarization state of an optical reception signal modulated by QPSK (Quadrature Phase-Shift Keying). The system of Non-Patent Document 1 calculates multiple Jones vectors from the optical reception signal and maps each of the calculated Jones vectors to a point in Stokes space. Next, the system of Non-Patent Document 1 divides the multiple points obtained by mapping into four groups and calculates the center point of each group. Furthermore, the system of Non-Patent Document 1 calculates a normal vector based on the four calculated center points. The system of Non-Patent Document 1 monitors the polarization state of the optical reception signal based on the rotation speed of the normal vector calculated in this way. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Jingnan Li, Yangyang Fan, Zhenning Tao, Hisao Nakashima, and Takeshi Hoshida, "Polarization Change Monitor Based on Geometrical Analysis in Stokes Space", 2021 European Conference on Optical Communication (ECOC), November 22, 2021 [Non-Patent Document 2] Bogdan Szafraniec, Todd S. Marshall, and Bernd Nebendahl, "Performance Monitoring and Measurement Techniques for Coherent Optical Systems," Journal of Lightwave Technology, February 15, 2013, vol. 31, no. 4, pp. 648-663. Summary of the Invention [Problem to be solved by the invention]

[0004] The inventors of the present disclosure have discovered a new technique for monitoring the polarization state of a received optical signal. It is an object of the present disclosure to provide a new technique for monitoring the polarization state of a received optical signal. [Means for solving the problem]

[0005] The polarization state monitoring device of the present disclosure includes an identification means for identifying a first polarization state vector representing the polarization state of the optical reception signal in each of a plurality of first partial periods obtained from a monitoring period, and for identifying a second polarization state vector representing the polarization state of the optical reception signal in each of a plurality of second partial periods obtained from the monitoring period; a calculation means for calculating a rotation angle of the first polarization state vector for each of a plurality of pairs of the first polarization state vectors, and for calculating the rotation angle of the second polarization state vector for each of a plurality of pairs of the second polarization state vectors; a determination means for determining whether or not the length of the first partial period or the length of the interval of the first partial period is appropriate based on the rotation angle of the first polarization state vector and the rotation angle of the second polarization state vector; and an output means for outputting rate of change data representing the speed of change of the polarization state during the monitoring period, based on the rotation angle of the first polarization state vector, when it is determined that the length of the first partial period or the length of the interval of the first partial period is appropriate. The length of the second sub-period is shorter than the length of the first sub-period, or the length of an interval of the second sub-period is shorter than the length of an interval of the first sub-period.

[0006] A polarization state monitoring method according to the present disclosure is executed by a computer and includes the steps of: identifying a first polarization state vector representing the polarization state of an optical reception signal in each of a plurality of first partial periods obtained from a monitoring period, and identifying a second polarization state vector representing the polarization state of an optical reception signal in each of a plurality of second partial periods obtained from the monitoring period, calculating a rotation angle of the first polarization state vector for each of a plurality of pairs of the first polarization state vector, and calculating a rotation angle of the second polarization state vector for each of a plurality of pairs of the second polarization state vector, determining whether or not a length of the first partial period or a length of an interval of the first partial period is appropriate based on the rotation angle of the first polarization state vector and the rotation angle of the second polarization state vector, and outputting change rate data representing a speed of change of the polarization state in the monitoring period based on the rotation angle of the first polarization state vector when it is determined that the length of the first partial period or the length of the interval of the first partial period is appropriate. The length of the second sub-period is shorter than the length of the first sub-period, or the length of an interval of the second sub-period is shorter than the length of an interval of the first sub-period.

[0007] The program of the present disclosure causes a computer to execute the polarization state monitoring method of the present disclosure. Effect of the Invention

[0008] According to the present disclosure, a new technique for monitoring the polarization state of a received optical signal is provided. [Brief description of the drawings]

[0009] [Figure 1] 1 is a diagram illustrating an optical transmission and reception system handled by a polarization state monitoring device according to the present disclosure; [Diagram 2] 1 is a diagram illustrating an example of an outline of the operation of a polarization state monitoring device; [Diagram 3] FIG. 13 is a diagram illustrating aliasing with respect to the rotation angle of the polarization state. [Figure 4] 1 is a first block diagram illustrating a functional configuration of a polarization state monitoring device; [Diagram 5] FIG. 2 is a block diagram illustrating a hardware configuration of a computer that realizes the polarization state monitoring device. [Figure 6] 4 is a first flowchart illustrating the flow of processing executed by the polarization state monitoring device. [Figure 7] FIG. 13 is a diagram illustrating a situation in which the length of an interval in a first partial period is different from the length of an interval in a second partial period. [Figure 8] FIG. 2 is a second block diagram illustrating a functional configuration of the polarization state monitoring device. [Figure 9] 10 is a second flowchart illustrating the flow of processing executed by the polarization state monitoring device. [Figure 10] 10 is a third flowchart illustrating the flow of processing executed by the polarization state monitoring device. [Figure 11] FIG. 2 is a diagram illustrating a first partial period, a second partial period, and a third partial period. [Figure 12] 13 is a fourth flowchart illustrating the flow of processing executed by the polarization state monitoring device. [Figure 13] 13 is a fourth flowchart illustrating the flow of processing executed by the polarization state monitoring device. [Figure 14] 10 is a fifth flowchart illustrating the flow of processing executed by the polarization state monitoring device. [Figure 15] 10 is a fifth flowchart illustrating the flow of processing executed by the polarization state monitoring device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. In each drawing, the same or corresponding elements are given the same reference numerals, and duplicated explanations are omitted as necessary for clarity of explanation. Furthermore, unless otherwise specified, predetermined values ​​such as predetermined values ​​and threshold values ​​are stored in advance in a storage device accessible from a device that uses the values. Furthermore, unless otherwise specified, the storage unit is composed of one or more arbitrary number of storage devices.

[0011] [Embodiment 1] <Summary> 1 is a diagram illustrating an optical transmission and reception system handled by the polarization state monitoring device of the present disclosure. The optical transmission and reception system 1 includes a transmission device 100, a reception device 200, and an optical communication path 300. The reception device 200 receives an optical signal transmitted from the transmission device 100 via the optical communication path 300. The optical communication path 300 is a communication path capable of transmitting an optical signal, and is configured using, for example, an optical fiber. Here, the optical signal transmitted from the transmission device 100 and the optical signal received by the reception device 200 are called an optical transmission signal 10 and an optical reception signal 20, respectively.

[0012] Communication between the transmitting device 100 and the receiving device 200 is performed, for example, as follows. The transmitting device 100 generates an optical transmission signal 10 from data (hereinafter, a message) to be transmitted to the receiving device 200. Specifically, the transmitting device 100 divides the message into a plurality of frames and generates a symbol string by encoding the data of each frame into a symbol. Then, the transmitting device 100 generates a polarization-multiplexed optical transmission signal 10 by modulating the X polarization and the Y polarization of an optical carrier, respectively, based on the symbol string.

[0013] The receiving device 200 recovers the message from the optical receiving signal 20. To do so, the receiving device 200 converts the optical receiving signal 20 into a digital signal. The receiving device 200 further divides the digital signal into a plurality of frames and converts each frame into a symbol to obtain a symbol string. The receiving device 200 then obtains the message by decoding each symbol in the symbol string.

[0014] Fig. 2 is a diagram illustrating an outline of the operation of the polarization state monitoring device 2000. Here, Fig. 2 is a diagram for facilitating understanding of the outline of the polarization state monitoring device 2000, and the operation of the polarization state monitoring device 2000 is not limited to that shown in Fig. 2.

[0015] The polarization state monitoring device 2000 monitors the state of polarization (SOP) of the optical reception signal 20. Specifically, the polarization state monitoring device 2000 handles change rate data representing the speed of change of the polarization state of the optical reception signal 20 during a monitoring period as one of the indices for monitoring the change of the polarization state of the optical reception signal 20.

[0016] The monitoring period can be determined arbitrarily. For example, a period during which the polarization state monitoring device 2000 receives the optical reception signal 20 can be divided into a plurality of monitoring periods of a predetermined length.

[0017] Hereinafter, the monitoring period for which the polarization state monitoring device 2000 calculates the change rate data is called the target monitoring period. For example, when the polarization state monitoring device 2000 calculates the change rate data for the i-th monitoring period, the i-th monitoring period is called the target monitoring period. The polarization state monitoring device 2000 attempts to calculate the change rate data for each of the multiple monitoring periods in order by treating the multiple monitoring periods as the target monitoring periods in chronological order.

[0018] The polarization state of the optical reception signal 20 can be represented by a vector in the Stokes space. Hereinafter, the vector in the Stokes space representing the polarization state of the optical reception signal 20 is called the "polarization state vector (SOP vector)". The polarization state vector is a vector whose starting point is the origin of the Stokes space and whose ending point is a point in the Stokes space representing the polarization state of the optical reception signal 20. Hereinafter, the point in the Stokes space representing the polarization state of the optical reception signal 20 is called the "polarization state point".

[0019] The magnitude of the change in the polarization state can be expressed by the rotation angle of the polarization state vector. The rotation angle of the polarization state vector is called the polarization state rotation angle (SOP rotation angle). For example, assume that the polarization state of the optical reception signal 20 changes from a state represented by a polarization state vector v1 to a state represented by a polarization state vector v2. In this case, the magnitude of the change in the polarization state of the optical reception signal 20 is expressed by the polarization state rotation angle from v1 to v2 (in other words, the angle between v1 and v2).

[0020] The polarization state monitoring device 2000 performs the following process on the optical reception signal 20 in the target monitoring period. For each of a plurality of first partial periods obtained from the target monitoring period, the polarization state monitoring device 20 identifies a polarization state vector that represents the polarization state of the optical reception signal 20 in that first partial period. Similarly, for each of a plurality of second partial periods obtained from the target monitoring period, the polarization state monitoring device 20 identifies a polarization state vector that represents the polarization state of the optical reception signal 20 in that second partial period. Hereinafter, the polarization state vector calculated for the first partial period and the polarization state vector calculated for the second partial period are referred to as the first polarization state vector and the second polarization state vector, respectively.

[0021] The length of the target monitoring period and the length of the first partial period are denoted as P0 and P1, respectively. In this case, if no interval is provided during the first partial period, [P0 / P1] number of first partial periods can be obtained from the target monitoring period. Here, [x] represents the largest integer less than or equal to x. Hereinafter, the number of the first partial periods included in the target monitoring period is denoted as N.

[0022] The length of the second partial period is shorter than the length of the first partial period. The length of the second partial period is denoted as P2. Also, the number of the second partial periods included in the target monitoring period is denoted as M. If no interval is provided between the second partial periods, M = [P0 / P2].

[0023] The length of the second partial period may be predetermined or may be calculated based on the length of the first partial period. In the latter case, for example, the polarization state monitoring device 2000 calculates the length P2 of the second partial period by multiplying a predetermined constant k1 by the length of the first partial period. That is, P2 = k1 * P1. k1 is a real number satisfying 0 < k1 < 1. Additionally, for example, the length P2 of the second partial period may be calculated by subtracting a predetermined constant k2 from the length P1 of the first partial period. k2 is a real number satisfying 0 < k2 < P1.

[0024] The polarization state monitoring device 2000 calculates the polarization state rotation angle for each of a plurality of pairs of the first polarization state vectors. For example, assume that the first polarization state vector in a certain first partial period is v1 and the first polarization state vector in the next first partial period is v2. In this case, the polarization state monitoring device 2000 calculates the angle formed by v1 and v2 to calculate the polarization state rotation angle for this pair of the two first partial periods. Similarly, the polarization state monitoring device 2000 also calculates the polarization state rotation angle for each of a plurality of pairs of the second polarization state vectors. Hereinafter, the polarization state rotation angle calculated for the pair of the first partial periods is called the first polarization state rotation angle. Also, the polarization state rotation angle calculated for the pair of the second partial periods is called the second polarization state rotation angle.

[0025] The polarization state monitoring device 2000 determines whether the length of the first partial period is appropriate based on the calculated first polarization state rotation angle and second polarization state rotation angle. If it is determined that the length of the first partial period is appropriate, the polarization state monitoring device 2000 outputs rate of change data for the target monitoring period using the first polarization state rotation angle.

[0026] If it is determined that the length of the first partial period is inappropriate, the polarization state monitoring device 2000 does not output the rate of change data. At this time, the polarization state monitoring device 2000 may output information indicating that the length of the first partial period is inappropriate (hereinafter, alert information).

[0027] <Examples of effects> The polarization state monitoring device 2000 calculates change rate data representing the speed of change of the polarization state as one of the indices for monitoring the polarization state of the optical reception signal 20 received by the reception device 200. As the change rate data, the speed of rotation of the polarization state vector, i.e., the rotation speed of the polarization state vector, is used.

[0028] The rotation speed of the polarization state vector can be calculated by dividing the rotation angle of the polarization state by the observation time. If the observation period is too long, the polarization state vector will rotate by more than 360° (so-called aliasing occurs), making it impossible to accurately calculate the rotation speed of the polarization state vector.

[0029] Figure 3 is a diagram illustrating aliasing with respect to the rotation angle of the polarization state. In the upper example, the polarization state vector at the start of the observation period is v1, and the polarization state vector at the end of the observation period is v2. The polarization state vector rotates 20° from v1 to v2.

[0030] On the other hand, in the lower example, the polarization state vector at the start of the observation period is v3, and the polarization state vector at the end of the observation period is v4. The polarization state vector rotates 380° from v3 to v4.

[0031] Here, the method of calculating the rotation angle using the polarization state vector at the start and end points of the observation period makes it impossible to distinguish between the upper and lower cases. Therefore, if the observation period is too long, as in the example at the bottom of Figure 3, the polarization state vector rotates by 360° or more during the observation period, making it impossible to accurately calculate the rotation angle of the polarization state vector. As a result, the change rate data cannot be calculated accurately either.

[0032] In this regard, the polarization state monitoring device 2000 uses the above-mentioned method to determine whether or not the length of the first partial period is appropriate. Then, if the length of the first partial period is appropriate, the polarization state rotation angle calculated for the first partial period is used to calculate the change rate data. Thus, the polarization state monitoring device 2000 calculates the change rate data when it is possible to accurately calculate the change rate data. Therefore, the polarization state monitoring device 2000 can obtain accurate change rate data.

[0033] The polarization state monitoring device 2000 of this embodiment will be described in more detail below.

[0034] <Example of functional configuration> 4 is a first block diagram illustrating a functional configuration of the polarization state monitoring device 2000. The polarization state monitoring device 2000 includes an identifying unit 2020, a calculating unit 2040, a determining unit 2060, and an output unit 2080. The identifying unit 2020 identifies a first polarization state vector for each of a plurality of first partial periods obtained from the target monitoring period. The identifying unit 2020 also identifies a second polarization state vector for each of a plurality of second partial periods obtained from the target monitoring period.

[0035] The calculation unit 2040 calculates the first polarization state rotation angle for each of the multiple pairs of the first polarization state vectors, and calculates the second polarization state rotation angle for each of the multiple pairs of the second polarization state vectors.

[0036] The determination unit 2060 determines whether the length of the first partial period is appropriate based on the calculated first polarization state rotation angle and second polarization state rotation angle. The output unit 2080 outputs the change rate data when it is determined that the length of the first partial period is appropriate.

[0037] <Example of hardware configuration> Each functional component of the polarization state monitoring device 2000 may be realized by hardware that realizes each functional component (e.g., a hardwired electronic circuit, etc.), or may be realized by a combination of hardware and software (e.g., a combination of an electronic circuit and a program that controls it, etc.). Below, a further description will be given of the case where each functional component of the polarization state monitoring device 2000 is realized by a combination of hardware and software.

[0038] 5 is a block diagram illustrating a hardware configuration of a computer 1000 that realizes the polarization state monitoring apparatus 2000. The computer 1000 is any computer. For example, the computer 1000 is a stationary computer such as a PC (Personal Computer) or a server machine. Alternatively, the computer 1000 is a portable computer such as a smartphone or a tablet terminal. Alternatively, the computer 1000 is a semiconductor chip such as a System on Chip (SoC). The computer 1000 may be a dedicated computer designed to realize the polarization state monitoring apparatus 2000, or may be a general-purpose computer.

[0039] For example, by installing a specific application in the computer 1000, each function of the polarization state monitoring device 2000 is realized by the computer 1000. The application is configured with a program for realizing each functional component of the polarization state monitoring device 2000. The program can be acquired by any method. For example, the program can be acquired from a storage medium (such as a DVD (Digital Versatile Disk) or a USB (Universal Serial Bus) memory) in which the program is stored. Alternatively, the program can be acquired by downloading the program from a server device that manages the storage device in which the program is stored.

[0040] The computer 1000 has a bus 1020, a processor 1040, a memory 1060, a storage device 1080, an input / output interface 1100, and a network interface 1120. The bus 1020 is a data transmission path for the processor 1040, the memory 1060, the storage device 1080, the input / output interface 1100, and the network interface 1120 to transmit and receive data to and from each other. However, the method of connecting the processor 1040 and the like to each other is not limited to a bus connection.

[0041] The processor 1040 is a processor such as a central processing unit (CPU), a graphics processing unit (GPU), a digital signal processor (DSP), or a field-programmable gate array (FPGA). The memory 1060 is a main storage device realized using a random access memory (RAM) or the like. The storage device 1080 is an auxiliary storage device realized using a hard disk, a solid state drive (SSD), a memory card, or a read only memory (ROM) or the like.

[0042] The input / output interface 1100 is an interface for connecting the computer 1000 to an input / output device. For example, the input / output interface 1100 is connected to an input device such as a keyboard and an output device such as a display device.

[0043] The network interface 1120 is an interface for connecting the computer 1000 to a network. This network may be a LAN (Local Area Network) or a WAN (Wide Area Network).

[0044] The storage device 1080 stores a program (a program for realizing the above-mentioned application) for realizing each functional component of the polarization state monitoring device 2000. The processor 1040 reads the program into the memory 1060 and executes it to realize each functional component of the polarization state monitoring device 2000.

[0045] The polarization state monitoring device 2000 may be realized by one computer 1000, or may be realized by multiple computers 1000. In the latter case, the configurations of the computers 1000 do not need to be the same, and may be different from each other.

[0046] The polarization state monitoring device 2000 may be realized integrally with the receiving device 200. In this case, each functional component of the polarization state monitoring device 2000 is implemented inside the receiving device 200. In this way, the receiving device 200 also functions as the polarization state monitoring device 2000.

[0047] <Processing flow> Fig. 6 is a first flowchart illustrating the flow of processing executed by the polarization state monitoring device 2000. A series of processing shown in Fig. 6 is executed sequentially for a plurality of monitoring periods.

[0048] The identifying unit 2020 identifies a first polarization state vector for each of a plurality of first partial periods obtained from a target monitoring period (S102). The calculating unit 2040 calculates a first polarization state rotation angle for each of a plurality of pairs of first polarization state vectors (S104).

[0049] The identifying unit 2020 identifies the second polarization state vector for each of the second partial periods obtained from the target monitoring period (S106). The calculating unit 2040 calculates the second polarization state rotation angle for each of the pairs of the second polarization state vectors (S108).

[0050] The determination unit 2060 determines whether the length of the first partial period is appropriate based on the calculated first polarization state rotation angles and second polarization state rotation angles (S110). If it is determined that the length of the first partial period is appropriate (S110: YES), the output unit 2080 outputs the change rate data (S112).

[0051] When it is determined that the length of the first partial period is not appropriate (S110: NO), various processes can be executed by the polarization state monitoring device 2000. For example, the polarization state monitoring device 2000 outputs a warning message indicating that the length of the first partial period is not appropriate. Alternatively, for example, the polarization state monitoring device 2000 may change the length of the first partial period as described in a second embodiment described later.

[0052] The flow of the process executed by the polarization state monitoring device 2000 is not limited to the flow shown in Fig. 6. For example, in Fig. 6, the process related to the first partial period (S102 and S104) and the process related to the second partial period (S106 and S108) are executed in parallel. However, these processes may be executed sequentially instead of in parallel. For example, after S102 and S104 are executed, S106 and S108 are executed.

[0053] <Specifying the polarization state vector: S102, S106> The identification unit 2020 identifies a first polarization state vector for each of the multiple first partial periods (S102). The identification unit 2020 also identifies a second polarization state vector for each of the multiple second partial periods (S106). In the following, the first partial period and the second partial period are collectively referred to as "partial periods", and several methods for identifying the polarization state vector are illustrated. In the following description, when the partial period represents the first partial period, the polarization state vector represents the first polarization state vector. On the other hand, when the partial period represents the second partial period, the polarization state vector represents the second polarization state vector.

[0054] <<Example 1 of how to determine the polarization state vector>> For example, the determination unit 2020 uses a polarimeter to determine the polarization state vector for each partial period. When a polarimeter is used to determine the polarization state vector, the polarimeter is installed in advance in the receiving device 200. The optical reception signal 20 is input to the polarimeter.

[0055] A polarimeter is a device that measures the polarization state of input light. For example, when an optical reception signal 20 is input, the polarimeter outputs time series data {S[t]} of the Stokes vector S that represents the polarization state of the optical reception signal 20. Here, t represents time. The Stokes vector S is a list of four types of Stokes parameters s0, s1, s2, and s3.

[0056] Stokes space is a three-dimensional space defined by three axes, s1, s2, and s3. Therefore, the polarization state vector v[t] of the optical reception signal 20 at time t can be expressed as v[t]=(s1[t],s2[t],s3[t]) using the three Stokes parameters s1[t], s2[t], and s3[t] output from the polarimeter to which the optical reception signal 20 at time t is input.

[0057] Therefore, the identifying unit 2020 acquires time-series data of the Stokes vector output from a polarimeter provided in the receiving device 200. Then, for each partial period, the identifying unit 2020 identifies a polarization state vector for that partial period using one or more Stokes vectors for that partial period.

[0058] For example, the determination unit 2020 obtains a representative Stokes vector S[rj] for each subperiod j. The time rj is, for example, a specific time point related to the subperiod j (such as the start or end of the subperiod j). Furthermore, the determination unit 2020 extracts Stokes parameters s1[rj], s2[rj], and s3[rj] from the representative Stokes vector S[rj]. Then, the determination unit 2020 determines the vector (s1[rj], s2[rj], s3[rj]) specified by these parameters as the polarization state vector of the subperiod j.

[0059] Alternatively, for example, the determination unit 2020 calculates statistical values ​​ss1[j], ss2[j], and ss3[j] of the Stokes parameters s1, s2, and s3, respectively, using a plurality of Stokes vectors for the partial period j. Then, the determination unit 2020 determines the vector (ss1[j], ss2[j], ss3[j]) specified by the calculated statistical values ​​as the polarization state vector for the partial period j.

[0060] There are various methods by which the identifying unit 2020 acquires the Stokes vector output from the polarimeter. For example, the receiving device 200 transmits the Stokes vector output from the polarimeter to the polarization state monitoring device 2000. In this case, the identifying unit 2020 acquires the Stokes vector by receiving the Stokes vector transmitted from the polarization state monitoring device 2000. As another example, the receiving device 200 stores the Stokes vector output from the polarimeter in a storage unit accessible from the polarization state monitoring device 2000. In this case, the identifying unit 2020 acquires the Stokes vector from this storage unit.

[0061] In addition, when only the representative Stokes vector is used to identify the polarization state vector, the receiving device 200 may be configured to transmit only the representative Stokes vector or to store only the representative Stokes vector in a memory unit.

[0062] <<Example 2 of how to determine the polarization state vector>> The determination unit 2020 obtains sample data representing the polarization state of the optical reception signal 20 in each frame of the optical reception signal 20. For example, the sample data is a Jones vector. Furthermore, the determination unit 2020 obtains a corresponding point for each sample data by mapping the sample data of each frame to a point in the Stokes space.

[0063] From the sample data at time t, the Stokes vector S[t]=(s0[t],s1[t],s2[t],s3[t]) can be obtained. Therefore, the identification unit 2020 obtains a point (s1[t],s2[t],s3[t]) as a corresponding point corresponding to the sample data at time t.

[0064] The Stokes vector S[t] at time t can be calculated using the sample data at time t as follows:

number

[0065] Here, the number of frames included in the optical reception signal 20 in each partial period is denoted as n. In this case, the identification unit 2020 calculates one polarization state vector for each partial period based on n corresponding points obtained for the n frames included in that partial period. Hereinafter, a set of corresponding points obtained for multiple frames included in a partial period is referred to as a corresponding point group corresponding to that frame. The corresponding point group for each frame includes n corresponding points.

[0066] For example, the determination unit 2020 performs the following process for each partial period. First, the determination unit 2020 calculates a plane in the Stokes space that fits the corresponding point group obtained for the target partial period (in other words, fits n corresponding points included in the corresponding point group). The determination unit 2020 determines, as a polarization state vector, a vector whose end point is the intersection point of the normal vector of the plane and the Poincaré sphere and whose start point is the origin of the Stokes space.

[0067] Here, the normal vector is determined to pass through the origin of the Stokes space. In addition, there may be two normal vectors passing through a specific point on a certain plane. Therefore, it is assumed that a rule for selecting a normal vector to be used for calculating a polarization state point from these two normal vectors is determined in advance.

[0068] Here, the plane in the Stokes space can be expressed as follows.

number

[0069] From this, for example, the identification unit 2020 uses the corresponding point group to calculate A, B, C, and D that satisfy formula (2), thereby calculating a plane that fits the corresponding point group. For example, the identification unit 2020 substitutes each corresponding point included in the corresponding point group into formula (2) and performs singular value decomposition (SVD). As a result, A, B, C, and D in formula (2) are calculated, and a plane that fits the corresponding point group is calculated.

[0070] Here, when QAM (Quadrature Amplitude Modulation) is used, the corresponding points are located inside a lens-shaped area that is a combination of an area defined by the following formula (3) and an area defined by the following formula (4).

number

number

[0071] The derivation of equation (3) is disclosed in Non-Patent Document 2. In the derivation of equation (3), for the H polarization state, the point with the maximum amplitude is selected. For the V polarization state, all points within a unit circle on the imaginary plane are considered. This is expressed by the Jones vector:

number

[0072] Equation (3) is obtained by converting the Jones vectors in equation (5) into Stokes vectors.

[0073] In contrast, in the derivation of equation (4), for the V polarization state, the point with the maximum amplitude is selected, and for the H polarization state, any point within the unit circle on the imaginary plane is considered. This is expressed by the Jones vector:

number

[0074] Equation (4) is obtained by converting the Jones vectors in equation (6) into Stokes vectors.

[0075] From equations (3) and (4), the above lens-shaped region is a point-symmetric region with the origin as the center. Therefore, a plane that fits the corresponding points distributed inside this lens-shaped region passes through the origin. Therefore, we can assume that D=0 in equation (2).

[0076] Therefore, the specification unit 2020 may calculate a plane that fits the corresponding points by calculating A, B, and C that satisfy the following, using the corresponding points:

number

[0077] When formula (7) is used, a plane that fits the corresponding points can be calculated by a method such as singular value decomposition, just like when formula (2) is used.

[0078] The method of calculating one polarization state vector based on multiple corresponding points is not limited to the above-mentioned method of using a plane that fits multiple corresponding points. For example, the determination unit 2020 may use the method disclosed in Non-Patent Document 1 to calculate one corresponding point based on multiple corresponding points and calculate a polarization state vector that has the calculated corresponding point as its end point.

[0079] There are various methods for the identifying unit 2020 to acquire sample data. For example, the receiving device 200 is configured to generate sample data for each frame of the optical reception signal 20 and transmit the generated sample data to the polarization state monitoring device 2000. In this case, the identifying unit 2020 acquires the sample data by receiving the sample data transmitted from the polarization state monitoring device 2000. As another example, the receiving device 200 is configured to store the sample data generated for each frame of the optical reception signal 20 in a storage unit accessible from the polarization state monitoring device 2000. In this case, the identifying unit 2020 acquires the sample data from this storage unit.

[0080] Note that, when the specifying unit 2020 obtains sample data only for the representative frame, the receiving device 200 may be configured to generate sample data only for the representative frame.

[0081] <Calculation of polarization state rotation angle: S104, S108> The calculation unit 2040 calculates the first polarization state rotation angle for each of the multiple pairs of the first polarization state vector (S104). The calculation unit 2040 also calculates the second polarization state rotation angle for each of the multiple pairs of the second polarization state vector (S108). Hereinafter, the first polarization state rotation angle and the second polarization state rotation angle are collectively referred to as "polarization state rotation angle", and a calculation method of the polarization state rotation angle will be described. In the following description, the first polarization state vector and the second polarization state vector are collectively referred to as the polarization state vector. When the polarization state vector means the first polarization state vector, the polarization state rotation angle means the first polarization state rotation angle. On the other hand, when the polarization state vector means the second polarization state vector, the polarization state rotation angle means the second polarization state rotation angle.

[0082] A pair of polarization state vectors is composed of adjacent polarization state vectors in time series data of the polarization state vectors (plurality of polarization state vectors arranged in time series). For example, a set of pairs of polarization state vectors {(v[1],v[2]),(v[2],v[3]),...,(v[m-1],v[m])} is obtained from the time series data of the polarization state vectors (v[1],v[2],v[3]),...,(v[m-1],v[m]).

[0083] The polarization state monitoring device 2000 calculates the polarization state rotation angle for each pair included in this set. Specifically, the polarization state monitoring device 2000 calculates the polarization state rotation angle a[1] for the polarization state vector pair (v[1],v[2]), the polarization state rotation angle a[2],...,a[m-1] for the polarization state rotation angle pair (v[m-1],v[m]). As a result, the time series data (a[1],a[2],...,a[m-1]) of the polarization state rotation angle is obtained for the set of polarization state vector pairs {(v[1],v[2]),(v[2],v[3]),...,(v[m-1],v[m])}. Here, the i-th polarization state rotation angle a[i] is calculated by calculating the angle between the polarization state vectors v[i] and v[i+1].

[0084] <Determining the appropriateness of the length of the first partial period: S110> The determination unit 2060 determines whether the length of the first partial period is appropriate using the first polarization state rotation angle and the second polarization state rotation angle (S110). Usually, the magnitude of the first polarization state rotation angle relative to the second polarization state angle increases in proportion to the length of the first partial period relative to the length of the second partial period. However, if the first partial period is too long, aliasing occurs and this proportional relationship no longer holds.

[0085] Therefore, for example, the determination unit 2060 determines whether the length of the first partial period is appropriate by using a condition that is satisfied when the proportional relationship described above is satisfied. For example, the determination unit 2060 calculates an index value I1 defined by the following formula (8).

number

[0086] Here, theoretically, in a situation where the above-mentioned proportional relationship holds, I1 is 0, and in a situation where the above-mentioned proportional relationship does not hold, I1 is a value greater than 0. However, in reality, even in a situation where the above-mentioned proportional relationship holds, I1 may be a value greater than 0 due to an error or the like.

[0087] Therefore, for example, the determination unit 2060 determines whether the index value I1 is equal to or greater than a predetermined threshold value α. The threshold value α satisfies 0<α<1. If the index value I1 is equal to or greater than the threshold value α, the determination unit 2060 determines that the length of the first partial period is inappropriate (S110: NO). On the other hand, if the index value I1 is less than the threshold value α, the determination unit 2060 determines that the length of the first partial period is appropriate (S110: YES).

[0088] Here, the value of the threshold value α is assumed to be determined in advance. The method for determining the value of α is arbitrary. For example, α is set to a value closer to 0 as the accuracy of the calculation by the polarization state monitoring device 2000 increases (the calculation error is smaller). α may also be determined based on the length of a partial period.

[0089] <Output of rate of change data: S112> When it is determined that the length of the first partial period is appropriate, the output unit 2080 outputs the change rate data (S112). To this end, the output unit 2080 calculates the change rate data.

[0090] As described below, there are various methods for calculating the change rate data. For example, the output unit 2080 is configured in advance to calculate the change rate data by a specific method. Alternatively, for example, the output unit 2080 may dynamically select a calculation method to be used from a plurality of calculation methods and calculate the change rate data by the selected method.

[0091] Below, some specific examples of the method of calculating the rate of change data will be given.

[0092] <<Example 1 of how to calculate rate of change data>> For example, the output unit 2080 calculates a rotation angle per unit time (i.e., a rotation speed) for each of the multiple first polarization state rotation angles calculated by the calculation unit 2040. Then, the output unit 2080 calculates a statistical value (e.g., an average value) of the multiple calculated rotation speeds as change speed data in the target monitoring period. Hereinafter, this calculation method will be referred to as an adjacent method.

[0093] It is assumed that the time series data of the first polarization state vector (v1[1], v1[2], ..., v1[N]) is obtained by the determination unit 2020. Also, the time series data of the first polarization state rotation angle (a1[1], a1[2], ..., a1[N-1]) is obtained by the calculation unit 2040.

[0094] The output unit 2080 calculates the rotation speed w[i] from each first polarization state rotation angle a1[i]. As a result, time series data of the rotation speed (w[1], w[2], ..., w[N-1]) is obtained. Then, the output unit 2080 calculates the average value wo of the rotation speeds w[1], w[2], ..., w[N-1] as the change speed data during the target monitoring period.

[0095] The rotation speed w[i] can be calculated by dividing the first polarization state rotation angle a1[i] by the observation time. Specifically, it can be calculated using the following equation (9).

number

[0096] If there are no intervals between the first sub-periods, the observation time is equal to the length P1 of the first sub-periods, whereas if there are intervals between the first sub-periods, the observation time is equal to the sum of the length P1 of the first sub-periods and the length of the intervals between the first sub-periods.

[0097] <<Example 2 of how to calculate rate of change data>> The output unit 2080 calculates the change rate data for the target monitoring period from the polarization state vectors at the beginning and end of the time series among the first polarization state vectors calculated for the target monitoring period. That is, the output unit 2080 calculates the angle between the leading polarization state vector and the trailing polarization state vector, and divides the angle by the observation time to calculate the change rate data for the target monitoring period. Hereinafter, this calculation method is called the head-to-tail method.

[0098] It is assumed that the time series data (v1[1],v1[2],...,v1[N]) of the first polarization state vector has been obtained. The output unit 2080 calculates the angle between the first polarization state vector v1[1] and the last polarization state vector v1[N]. The output unit 2080 then calculates the change rate data wo by dividing the calculated angle by the observation time. Using the symbol t used in equation (9), the observation time can be expressed as t[N]-t[1].

[0099] <<Example of selection method>> For example, the calculation unit 2040 selects either the adjacent method or the head-to-tail method based on the sum of the first polarization state rotation angles (a1[1] + a1[2] + ... + a1[N-1]). More specifically, the calculation unit 2040 selects the adjacent method when the sum of the first polarization state rotation angles is equal to or greater than a threshold. On the other hand, the calculation unit 2040 selects the head-to-tail method when the sum of the first polarization state rotation angles is less than the threshold. This threshold is, for example, π / 2.

[0100] <Cases where the length of the first partial period is inappropriate> When it is determined that the length of the first partial period is inappropriate, the polarization state monitoring device 2000 may perform various processes. For example, in response to determining that the length of the first partial period is inappropriate, the polarization state monitoring device 2000 may start a process for the next monitoring period. At this time, the polarization state monitoring device 2000 may generate and output alert information indicating that "the length of the first partial period is inappropriate."

[0101] <How to use rate of change data> The polarization state monitoring device 2000 calculates the change rate data for each monitoring period. This provides time-series data of the change rate data. The time-series data of the change rate data can be used for detecting an abnormality in the polarization state of the optical reception signal 20.

[0102] For example, the polarization state monitoring device 2000 detects an abnormality in the polarization state of the optical reception signal 20 by detecting an abnormal value from the time series data of the change rate data. For example, it is assumed that the polarization state monitoring device 2000 detects that the pth to qth change rate data have an abnormal value. In this case, the polarization state monitoring device 2000 determines that an abnormality has occurred in the polarization state of the optical reception signal 20 from the pth monitoring period to the qth monitoring period. Here, various existing technologies can be used as a technology for detecting an abnormal value from the time series data.

[0103] <How to use the results of detecting abnormalities in the polarization state> The detection of an abnormality in the polarization state of the optical reception signal 20 can be utilized in various ways. For example, when it is found that the receiving device 200 is broken, the history of the analysis of the polarization state of the optical reception signal 20 in the receiving device 200 (for example, the history of the time series data of the angular velocity and the time series data of the statistical values ​​of the angular velocity described above) can be used to investigate the cause of the failure of the receiving device 200. For example, it is assumed that an abnormality in the polarization state of the optical reception signal 20 is detected at a certain point in time before the receiving device 200 breaks down. In this case, it is considered that an event that causes an abnormality in the polarization state of the optical reception signal 20, such as a lightning strike, is related to the failure of the receiving device 200.

[0104] Alternatively, for example, an abnormality in the receiving device 200 may be predicted by monitoring the polarization state of the optical reception signal 20. For example, if an abnormality occurs in the polarization state of the optical reception signal 20, there is a possibility that an abnormality will occur in the receiving device 200 afterwards. Therefore, for example, if an abnormality in the polarization state is detected for the optical reception signal 20 received by the receiving device 200, a receiving device other than the receiving device 200 is used to receive a message from the transmitting device 100.

[0105] <Modification> Instead of making the length of the first sub-period longer than the length of the second sub-period, the length of the interval of the first sub-period may be longer than the length of the interval of the second sub-period. Figure 7 shows a situation where the length of the interval of the first sub-period and the length of the interval of the second sub-period are different from each other. In Figure 7, the diagonal lines on the right side represent the interval of the first sub-period. The diagonal lines on the left side represent the interval of the second sub-period.

[0106] The length P1 of the first subperiod and the length P2 of the second subperiod are equal to each other (P1=P2), while the length Q1 of the interval of the first subperiod is longer than the length Q2 of the interval of the second subperiod (Q1>Q2).

[0107] The determination unit 2060 determines whether or not the interval length of the first partial period is appropriate, instead of whether or not the length of the first partial period is appropriate. The specific method of this determination is the same as the method of determining whether or not the length of the first partial period is appropriate, described above.

[0108] For example, the determination unit 2060 determines whether the index value I1 is equal to or greater than a threshold value α. If I1≧α, the determination unit 2060 determines that the interval length of the first partial period is appropriate. On the other hand, if I1<α, the determination unit 2060 determines that the interval length of the first partial period is inappropriate.

[0109] [Embodiment 2] 8 is a second block diagram illustrating a functional configuration of the polarization state monitoring apparatus 2000. The polarization state monitoring apparatus 2000 illustrated in FIG.

[0110] The polarization state monitoring apparatus 2000 of the second embodiment changes the length of the first partial period in response to determining that the length of the first partial period is inappropriate. The change in the length of the first partial period is performed by the change unit 2100.

[0111] As described above, the polarization state monitoring device 2000 attempts to calculate the rate of change data for each of the multiple monitoring periods in sequence. Therefore, when the length of the first partial period is changed in processing for a certain monitoring period, the length changed by the change unit 2100 is used as the length of the first partial period in processing for the next monitoring period and thereafter.

[0112] Therefore, according to the polarization state monitoring device 2000, in the case of sequentially monitoring the polarization states in a plurality of monitoring periods, when it is determined that the length of the first partial period is inappropriate in a certain monitoring period, the probability that the length of the first partial period is appropriate in the subsequent monitoring periods can be increased. Thus, according to the polarization state monitoring device 2000, compared with the case where the length of the first partial period is not changed, accurate change rate data can be calculated for more monitoring periods.

[0113] In addition, for each monitoring period, the polarization state monitoring device 2000 may repeat the processing for that monitoring period until the length of the first partial period becomes appropriate. By doing so, accurate change rate data can be calculated for all monitoring periods.

[0114] Here, according to the method described in Embodiment 1, the case where it is determined that the length of the first partial period is inappropriate is a case where the length of the first partial period is longer than the appropriate length. Therefore, the changing unit 2100 shortens the length of the first partial period.

[0115] There are various specific methods for shortening the length of the first partial period. For example, the changing unit 2100 sets a value obtained by multiplying the current length P1 of the first partial period by a predetermined number d1 (that is, d1*P1) as the new length of the first partial period. d1 is a real number satisfying 0 < d1 < 1.

[0116] In addition, for example, the changing unit 2100 sets a value obtained by subtracting a predetermined number d2 from the current length P1 of the first partial period (that is, P1 - d2) as the new length of the first partial period. d2 is a real number satisfying 0 < d2 < P1.

[0117] The change unit 2100 may change the length of the second partial period in accordance with the change in the length of the first partial period. For example, as described above, the length P2 of the second partial period is a value obtained by multiplying the length P1 of the first partial period by a constant k1. In this case, the change unit 2100 multiplies the changed length of the first partial period by k1 to set the new length of the second partial period as the value obtained by multiplying the changed length of the first partial period by k1.

[0118] <Example of hardware configuration> 5, similar to the hardware configuration of the polarization state monitoring apparatus 2000 of the embodiment 1. However, the storage device 1080 of the embodiment 2 stores a program for realizing each functional component of the polarization state monitoring apparatus 2000 of the embodiment 2.

[0119] <Processing flow> Fig. 9 is a second flowchart illustrating the flow of processing executed by polarization state monitoring device 2000. The processing in Fig. 9 is executed for each monitoring period. S102 to S112 in Fig. 9 are the same as S102 to S112 in Fig. 6, respectively. When it is determined that the length of the first partial period is not appropriate (S110: NO), changing unit 2100 shortens the length of the first partial period (S202).

[0120] As described above, the polarization state monitoring device 2000 may change the length of the first partial period in the processing for a certain monitoring period, and then may perform the processing for that monitoring period again. In other words, the processing shown in FIG. 9 may be repeated until the length of the first partial period becomes appropriate.

[0121] Fig. 10 is a third flowchart illustrating the flow of processing executed by the polarization state monitoring device 2000. In the flowchart of Fig. 10, after S202 is executed, the processing is executed again from the beginning of the flowchart. Thus, the processing of the third flowchart is repeated for one monitoring period until the length of the first partial period becomes appropriate.

[0122] <Modification> As described above, instead of making the length of the first partial period longer than the length of the second partial period, the length of the interval of the first partial period may be made longer than the length of the interval of the second partial period. In this case, when it is determined that the length of the interval of the first partial period is not appropriate, the change unit 2100 shortens the length of the interval of the first partial period.

[0123] The method for shortening the interval length Q1 of the first partial period is similar to the method for shortening the interval length P1 of the first partial period. For example, the change unit 2100 calculates the new interval length of the first partial period by multiplying the interval length Q1 of the first partial period by the constant d1 described above.

[0124] [Embodiment 3] The polarization state monitoring device 2000 of the third embodiment performs the following processes: 1) outputting rate of change data without changing the length of the first partial period, 2) shortening the length of the first partial period, or 3) lengthening the length of the first partial period. To this end, the polarization state monitoring device 2000 calculates the polarization state rotation angle not only for the first and second partial periods, but also for the third partial period whose length is longer than the first partial period.

[0125] 11 is a diagram illustrating a first partial period, a second partial period, and a third partial period. As shown in FIG. 11, the third partial period is shorter than the first partial period. Therefore, the first partial period is longer than the second partial period and shorter than the third partial period.

[0126] Specifically, the polarization state monitoring device 2000 operates as follows. The identification unit 2020 identifies a polarization state vector for each of a plurality of third partial periods obtained from the target monitoring period (S302). The length of the third partial period is denoted as P3. The number of second partial periods included in the target monitoring period is denoted as L. If no interval is provided between the third partial periods, L=[P0 / P3]. The polarization state vector identified for the third partial period is denoted as the third polarization state vector.

[0127] The length of the third partial period may be predetermined, or may be calculated based on the length of the first partial period. In the latter case, for example, the polarization state monitoring device 2000 calculates the length P3 of the third partial period by multiplying the length of the third partial period by a predetermined constant u1. That is, P3=u1*P1, where u1 is a real number greater than 1. Alternatively, for example, the length P3 of the third partial period may be calculated by adding a predetermined constant u2 to the length P1 of the first partial period (P3=P1+u2), where u2 is a real number greater than 0.

[0128] Figures 12 and 13 are a fourth flowchart illustrating the flow of processing executed by the polarization state monitoring device 2000. In the flowcharts shown in Figures 12 and 13, steps S102 to S112 are the same as steps S102 to S112 in the flowchart shown in Figure 6. In the flowcharts shown in Figures 12 and 13, step S202 is the same as step S202 in the flowchart shown in Figure 9.

[0129] The calculation unit 2040 calculates the polarization state rotation angle for each of the pairs in the third partial period (S304). The polarization state rotation angle calculated for the third partial period is referred to as a third polarization state rotation angle.

[0130] The processes for calculating the first polarization state rotation angle (S102 and S104) and the processes for calculating the second polarization state rotation angle (S106 and S108) are both performed in the same manner as in the first embodiment.

[0131] The determination unit 2060 determines whether or not the length of the first partial period is appropriate based on the first polarization state rotation angle and the second polarization state rotation angle (S110). If it is determined in S110 that the length of the first partial period is not appropriate (S110: NO), the change unit 2100 shortens the length of the first partial period (S202). Thus, the determination in S110 can also be expressed as "determination of whether or not the length of the first partial period is longer than an appropriate length."

[0132] If it is determined in S110 that the length of the first partial period is appropriate (S110: YES), the determination unit 2060 determines whether or not the length of the first partial period is appropriate based on the first polarization state rotation angle and the third polarization state rotation angle (S306). If it is determined in S306 that the length of the first partial period is not appropriate (S306: NO), the change unit 2100 lengthens the length of the first partial period (S308). Thus, the determination in S306 can also be expressed as "determination of whether or not the length of the first partial period is shorter than the appropriate length." Details of S306 and S308 will be described later.

[0133] If it is determined in S306 that the length of the first partial period is appropriate (S306: YES), the output unit 2080 outputs the change rate data (S112).

[0134] The flow of the process executed by the polarization state monitoring device 2000 is not limited to the flow shown in Figures 12 and 13. For example, the polarization state monitoring device 2000 may execute S110 after S306. In this case, when it is determined that the length of the first partial period is appropriate based on the first polarization state rotation angle and the third polarization state rotation angle, the polarization state monitoring device 2000 determines whether the length of the first partial period is appropriate based on the first polarization state rotation angle and the second polarization state rotation angle.

[0135] According to the polarization state monitoring device 2000 of the third embodiment, when the length of the first partial period is longer than the appropriate length, the length of the first partial period is changed to a shorter length. As a result, the length of the first partial period used in the subsequent monitoring periods is brought closer to the appropriate length. Also, when the length of the first partial period is shorter than the appropriate length, the length of the first partial period is changed to a longer length. As a result, the length of the first partial period used in the subsequent monitoring periods is brought closer to the appropriate length. Then, when the length of the first partial period is appropriate, the change rate data is output. Thus, according to the polarization state monitoring device 2000, the length of the first partial period is adaptively adjusted, and accurate change rate data is output for more monitoring periods.

[0136] The polarization state monitoring device 2000 may repeat the process for each monitoring period until the length of the first partial period becomes appropriate, thereby making it possible to calculate accurate change rate data for all monitoring periods.

[0137] 14 and 15 are a fifth flowchart illustrating the flow of processing executed by polarization state monitoring device 2000. In the fifth flowchart, after the length of the first partial period is changed in S202 or S308, the processing is executed again from the beginning of the flowchart. Therefore, in both S110 and S306, the processing of changing the length of the first partial period is repeated for one monitoring period until it is determined that the length of the first partial period is appropriate.

[0138] Here, in order to prevent the process from looping infinitely, the amount by which the length of the first partial period is increased in S308 is set to a value smaller than the amount by which the length of the first partial period is decreased in S202.

[0139] <Determination using the third polarization state rotation angle: S306> The determination unit 2060 determines whether the length of the first partial period is appropriate based on the first polarization state rotation angle and the third polarization state rotation angle (S306). Here, if the first polarization state rotation angle and the third polarization state rotation angle can be accurately calculated, the third polarization state rotation angle will be larger than the first polarization state rotation angle in proportion to the length of the third partial period relative to the length of the first partial period. However, if the first partial period is too short, the first polarization state rotation angle cannot be accurately calculated due to the influence of noise, etc., and the proportional relationship described above will no longer hold.

[0140] Therefore, for example, the determination unit 2060 determines whether the length of the first partial period is appropriate by determining whether the proportional relationship between the first polarization state rotation angle and the third polarization state rotation angle is correctly established. To this end, for example, the determination unit 2060 calculates an index value I2 defined by the following formula (10).

number

[0141] For example, the determination unit 2060 determines whether the index value I2 is equal to or greater than a predetermined threshold value β. The threshold value β satisfies 0<β<1. If the index value I2 is equal to or greater than the threshold value β, the determination unit 2060 determines that the length of the first partial period is appropriate (S306: YES). On the other hand, if the index value I2 is less than the threshold value β, the determination unit 2060 determines that the length of the first partial period is inappropriate (S306: NO).

[0142] The value of the threshold value β is assumed to be predetermined. The method for determining the value of β is arbitrary. For example, the value of β can be determined in the same manner as the method for determining the value of α.

[0143] <Process for lengthening the length of the first partial period: S308> If it is determined that the length of the first partial period is not appropriate based on the first polarization state rotation angle and the third polarization state rotation angle (S306: NO), the change unit 2100 lengthens the length of the first partial period (S308). There are various specific methods for lengthening the length of the first partial period. For example, the change unit 2100 multiplies the current length P1 of the first partial period by a predetermined constant r1 (i.e., r1*P1) as the new length of the first partial period. r1 is a real number greater than 1.

[0144] Alternatively, for example, the change unit 2100 may add a predetermined constant r2 to the length P1 of the current first partial period (i.e., P1+2) to set the new length of the first partial period. r2 is a real number greater than 0.

[0145] When the length of the first partial period is changed, the modification unit 2100 may modify the lengths of the second partial period and the third partial period in accordance with the change in the length of the first partial period. For example, the modification unit 2100 multiplies the new length of the first partial period by a constant k1 to obtain a new length of the second partial period. Similarly, the modification unit 2100 multiplies the new length of the first partial period by a constant u1 to obtain a new length of the third partial period.

[0146] <Example of functional configuration> The functional configuration of the polarization state monitoring device 2000 of the third embodiment is shown in, for example, Fig. 8, similarly to the functional configuration of the polarization state monitoring device 2000 of the second embodiment. However, the determination unit 2020 of the third embodiment determines a third polarization state vector for each of a plurality of third partial periods obtained from the target monitoring period, in addition to determining the first and second polarization state vectors. Furthermore, the calculation unit 2040 calculates a third polarization state rotation angle for each of a plurality of pairs in the third partial period, in addition to calculating the first and second polarization state rotation angles.

[0147] The determination unit 2060 determines whether the length of the first partial period is appropriate based on the first polarization state rotation angle and the second polarization state rotation angle. The determination unit 2060 also determines whether the length of the first partial period is appropriate based on the first polarization state rotation angle and the third polarization state rotation angle.

[0148] The output unit 2080 outputs the rate of change data when the length of the first partial period is determined to be appropriate based on the first polarization state rotation angle and the second polarization state rotation angle, and when the length of the first partial period is determined to be appropriate based on the first polarization state rotation angle and the third polarization state rotation angle.

[0149] When it is determined that the length of the first partial period is inappropriate based on the first polarization state rotation angle and the second polarization state rotation angle, the change unit 2100 lengthens the length of the first partial period. On the other hand, when it is determined that the length of the first partial period is inappropriate based on the first polarization state rotation angle and the third polarization state rotation angle, the change unit 2100 shortens the length of the first partial period.

[0150] <Example of hardware configuration> The polarization state monitoring apparatus 2000 of the third embodiment has, for example, a hardware configuration shown in Fig. 5, similar to the polarization state monitoring apparatus 2000 of the first embodiment and the polarization state monitoring apparatus 2000 of the second embodiment. However, the storage device 1080 of the third embodiment stores a program for realizing each functional component of the polarization state monitoring apparatus 2000 of the third embodiment.

[0151] <Modification> Instead of making the length of the first partial period, the length of the second partial period, and the length of the third partial period different from each other, the length of the interval of the first partial period, the length of the interval of the second partial period, and the length of the interval of the third partial period may be different from each other. In this case, the determination unit 2060 determines whether or not the length of the interval of the first partial period is appropriate based on the first polarization state rotation angle and the second polarization state rotation angle. Also, the determination unit 2060 determines whether or not the length of the interval of the first partial period is appropriate based on the first polarization state rotation angle and the third polarization state rotation angle. A specific method of this determination is the same as the method of determining whether or not the length of the first partial period is appropriate, described above.

[0152] For example, the determination unit 2060 calculates an index value I1 based on the first polarization state rotation angle and the second polarization state rotation angle, and determines whether the index value I1 is equal to or greater than a threshold value α. If I1≧α, the determination unit 2060 determines that the interval length of the first partial period is appropriate. On the other hand, if I1<α, the determination unit 2060 determines that the interval length of the first partial period is not appropriate.

[0153] Similarly, the determination unit 2060 calculates an index value I2 based on the first polarization state rotation angle and the third polarization state rotation angle, and determines whether the index value I2 is equal to or greater than a threshold value β. If I2≧β, the determination unit 2060 determines that the length of the interval of the first partial period is appropriate. On the other hand, if I2<β, the determination unit 2060 determines that the length of the interval of the first partial period is not appropriate.

[0154] When it is determined that the interval length of the first partial period is not appropriate based on the first polarization state rotation angle and the second polarization state rotation angle, the change unit 2100 shortens the interval length of the first partial period. The method of shortening the interval length Q1 of the first partial period is as described in the modification of the second embodiment.

[0155] When it is determined that the interval length of the first partial period is not appropriate based on the first polarization state rotation angle and the third polarization state rotation angle, the change unit 2100 lengthens the interval length of the first partial period. The method of lengthening the interval length Q1 of the first partial period is similar to the method of lengthening the interval length P1 of the first partial period. For example, the change unit 2100 calculates a new interval length of the first partial period by multiplying the interval length Q1 of the first partial period by the above-mentioned constant d1.

[0156] Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above-mentioned embodiments. Various modifications that can be understood by a person skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure. Furthermore, each embodiment can be appropriately combined with other embodiments.

[0157] Each drawing is merely an example for describing one or more embodiments. Each drawing may relate not only to one particular embodiment, but to one or more other embodiments. As can be understood by those skilled in the art, various features or steps described with reference to any one drawing may be combined with features or steps shown in one or more other drawings to create an embodiment not explicitly shown or described, for example. Not all features or steps shown in any one drawing are necessary to describe an exemplary embodiment, and some features or steps may be omitted. The order of steps described in any drawing may be changed as appropriate.

[0158] In the above example, the program includes a set of instructions (or software code) for making the computer perform one or more functions described in the embodiment when the program is loaded into the computer. The program may be stored in a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, the computer-readable medium or tangible storage medium includes random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, CD-ROM, digital versatile disc (DVD), Blu-ray (registered trademark) disk or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage device. The program may be transmitted on a transitory computer-readable medium or communication medium. By way of example and not limitation, the transitory computer-readable medium or communication medium includes electrical, optical, acoustic, or other forms of propagating signals.

[0159] A part or all of the above-described embodiments can be described as, but is not limited to, the following supplementary notes. (Appendix 1) an identification means for identifying a first polarization state vector representing the polarization state of the optical reception signal in each of a plurality of first partial periods obtained from the monitoring period, and for identifying a second polarization state vector representing the polarization state of the optical reception signal in each of a plurality of second partial periods obtained from the monitoring period; a calculation means for calculating a rotation angle of the first polarization state vector for each of a plurality of pairs of the first polarization state vector, and for calculating a rotation angle of the second polarization state vector for each of a plurality of pairs of the second polarization state vector; a determination means for determining whether or not a length of the first partial period or a length of an interval of the first partial period is appropriate based on a rotation angle of the first polarization state vector and a rotation angle of the second polarization state vector; and an output means for outputting change rate data representing a rate of change of the polarization state during the monitoring period based on a rotation angle of the first polarization state vector when it is determined that the length of the first partial period or the length of the interval of the first partial period is appropriate, A polarization state monitoring device, wherein the length of the second sub-period is shorter than the length of the first sub-period, or the length of an interval of the second sub-period is shorter than the length of an interval of the first sub-period. (Appendix 2) The polarization state monitoring device described in Appendix 1, wherein the determination means determines that the length of the first partial period or the length of the interval of the first partial period is appropriate when the rotation angle of the first polarization state vector and the rotation angle of the second polarization state vector are in a proportional relationship. (Appendix 3) 3. The polarization state monitoring device according to claim 1, further comprising a change means for changing a length of the first partial period when the length of the first partial period is not appropriate. (Appendix 4) the identifying means further identifies, for each of a plurality of third partial periods obtained from the monitoring period, a third polarization state vector representing a polarization state of the optical reception signal in the third partial period; The calculation means further calculates a rotation angle of the third polarization state vector for each of the plurality of pairs of the third polarization state vector, the determination means further determines whether or not a length of the first partial period or a length of an interval of the first partial period is appropriate based on a rotation angle of the first polarization state vector and a rotation angle of the third polarization state vector; the output means outputs the rate of change data when it is determined that a length of the first partial period or a length of an interval of the first partial period is appropriate based on a rotation angle of the first polarization state vector and a rotation angle of the second polarization state vector, and when it is determined that a length of the first partial period or a length of an interval of the first partial period is appropriate based on a rotation angle of the first polarization state vector and a rotation angle of the third polarization state vector, A polarization state monitoring device as described in Appendix 3, wherein the length of the third sub-period is longer than the length of the first sub-period, or the length of an interval of the third sub-period is longer than the length of an interval of the first sub-period. (Appendix 5) The change means is shortening a length of the first partial period when it is determined that the length of the first partial period is inappropriate based on the rotation angle of the first polarization state vector and the rotation angle of the second polarization state vector, or shortening a length of an interval of the first partial period when it is determined that the length of an interval of the first partial period is inappropriate based on the rotation angle of the first polarization state vector and the rotation angle of the second polarization state vector; 5. The polarization state monitoring device according to claim 4, further comprising: a step of lengthening a length of the first partial period when it is determined that the length of the first partial period is inappropriate based on the rotation angle of the first polarization state vector and the rotation angle of the third polarization state vector; or a step of lengthening a length of an interval of the first partial period when it is determined that the length of an interval of the first partial period is inappropriate based on the rotation angle of the first polarization state vector and the rotation angle of the third polarization state vector. (Appendix 6) The polarization state monitoring device described in Appendix 4, wherein the determination means determines that the length of the first partial period or the length of the interval of the first partial period is appropriate when the rotation angle of the first polarization state vector and the rotation angle of the third polarization state vector are in a proportional relationship. (Appendix 7) a step of identifying a first polarization state vector representing the polarization state of the optical reception signal in each of a plurality of first partial periods obtained from the monitoring period, and identifying a second polarization state vector representing the polarization state of the optical reception signal in each of a plurality of second partial periods obtained from the monitoring period; a calculation step of calculating a rotation angle of the first polarization state vector for each of a plurality of pairs of the first polarization state vector, and calculating a rotation angle of the second polarization state vector for each of a plurality of pairs of the second polarization state vector; a determining step of determining whether or not a length of the first partial period or a length of an interval of the first partial period is appropriate based on a rotation angle of the first polarization state vector and a rotation angle of the second polarization state vector; and an output step of outputting change rate data representing a rate of change of the polarization state during the monitoring period based on a rotation angle of the first polarization state vector when it is determined that the length of the first partial period or the length of the interval of the first partial period is appropriate, A computer-implemented polarization state monitoring method, wherein the length of the second sub-period is shorter than the length of the first sub-period, or the length of an interval of the second sub-period is shorter than the length of an interval of the first sub-period. (Appendix 8) 8. The polarization state monitoring method of claim 7, wherein in the determination step, if the rotation angle of the first polarization state vector and the rotation angle of the second polarization state vector are in a proportional relationship, it is determined that the length of the first partial period or the length of the interval of the first partial period is appropriate. (Appendix 9) 9. The polarization state monitoring method according to claim 7 or 8, further comprising a change step of changing a length of the first partial period when the length of the first partial period is not appropriate. (Appendix 10) In the identifying step, a third polarization state vector representing a polarization state of the optical reception signal in each of a plurality of third partial periods obtained from the monitoring period is further identified; In the calculation step, a rotation angle of the third polarization state vector is further calculated for each of the plurality of pairs of the third polarization state vector; In the determining step, it is further determined whether or not a length of the first partial period or a length of an interval of the first partial period is appropriate based on a rotation angle of the first polarization state vector and a rotation angle of the third polarization state vector; outputting the rate of change data when, in the output step, it is determined that the length of the first partial period or the length of the interval of the first partial period is appropriate based on the rotation angle of the first polarization state vector and the rotation angle of the second polarization state vector, and it is also determined that the length of the first partial period or the length of the interval of the first partial period is appropriate based on the rotation angle of the first polarization state vector and the rotation angle of the third polarization state vector; A polarization state monitoring method as described in Appendix 9, wherein the length of the third sub-period is longer than the length of the first sub-period, or the length of an interval of the third sub-period is longer than the length of an interval of the first sub-period. (Appendix 11) In the changing step, shortening a length of the first partial period when it is determined that the length of the first partial period is inappropriate based on the rotation angle of the first polarization state vector and the rotation angle of the second polarization state vector, or shortening a length of an interval of the first partial period when it is determined that the length of an interval of the first partial period is inappropriate based on the rotation angle of the first polarization state vector and the rotation angle of the second polarization state vector; The polarization state monitoring method according to claim 10, further comprising: lengthening a length of the first partial period when it is determined that the length of the first partial period is inappropriate based on the rotation angle of the first polarization state vector and the rotation angle of the third polarization state vector; or lengthening a length of an interval of the first partial period when it is determined that the length of an interval of the first partial period is inappropriate based on the rotation angle of the first polarization state vector and the rotation angle of the third polarization state vector. (Appendix 12) A polarization state monitoring method as described in Appendix 10, wherein in the determination step, if the rotation angle of the first polarization state vector and the rotation angle of the third polarization state vector are in a proportional relationship, it is determined that the length of the first partial period or the length of the interval of the first partial period is appropriate. (Appendix 13) a step of identifying a first polarization state vector representing the polarization state of the optical reception signal in each of a plurality of first partial periods obtained from the monitoring period, and identifying a second polarization state vector representing the polarization state of the optical reception signal in each of a plurality of second partial periods obtained from the monitoring period; a calculation step of calculating a rotation angle of the first polarization state vector for each of a plurality of pairs of the first polarization state vector, and calculating a rotation angle of the second polarization state vector for each of a plurality of pairs of the second polarization state vector; a determining step of determining whether or not a length of the first partial period or a length of an interval of the first partial period is appropriate based on a rotation angle of the first polarization state vector and a rotation angle of the second polarization state vector; an output step of outputting change rate data representing a rate of change of the polarization state during the monitoring period based on a rotation angle of the first polarization state vector when it is determined that the length of the first partial period or the length of the interval of the first partial period is appropriate; A program, wherein the length of the second sub-period is shorter than the length of the first sub-period, or the length of an interval of the second sub-period is shorter than the length of an interval of the first sub-period. (Appendix 14) The program described in Appendix 13, wherein in the determination step, if the rotation angle of the first polarization state vector and the rotation angle of the second polarization state vector are in a proportional relationship, it is determined that the length of the first partial period or the length of the interval of the first partial period is appropriate. (Appendix 15) 15. The program according to claim 13, further comprising a change step of changing a length of the first partial period if the length of the first partial period is not appropriate. (Appendix 16) In the identifying step, a third polarization state vector representing a polarization state of the optical reception signal in each of a plurality of third partial periods obtained from the monitoring period is further identified; In the calculation step, a rotation angle of the third polarization state vector is further calculated for each of the plurality of pairs of the third polarization state vector; In the determining step, it is further determined whether or not a length of the first partial period or a length of an interval of the first partial period is appropriate based on a rotation angle of the first polarization state vector and a rotation angle of the third polarization state vector; outputting the rate of change data when, in the output step, it is determined that the length of the first partial period or the length of the interval of the first partial period is appropriate based on the rotation angle of the first polarization state vector and the rotation angle of the second polarization state vector, and it is also determined that the length of the first partial period or the length of the interval of the first partial period is appropriate based on the rotation angle of the first polarization state vector and the rotation angle of the third polarization state vector; The program of claim 15, wherein the length of the third sub-period is longer than the length of the first sub-period, or the length of an interval of the third sub-period is longer than the length of an interval of the first sub-period. (Appendix 17) In the changing step, shortening a length of the first partial period when it is determined that the length of the first partial period is inappropriate based on the rotation angle of the first polarization state vector and the rotation angle of the second polarization state vector, or shortening a length of an interval of the first partial period when it is determined that the length of an interval of the first partial period is inappropriate based on the rotation angle of the first polarization state vector and the rotation angle of the second polarization state vector; The program described in Appendix 16, further comprising: increasing a length of the first partial period when it is determined that the length of the first partial period is inappropriate based on the rotation angle of the first polarization state vector and the rotation angle of the third polarization state vector; or increasing a length of an interval of the first partial period when it is determined that the length of an interval of the first partial period is inappropriate based on the rotation angle of the first polarization state vector and the rotation angle of the third polarization state vector. (Appendix 18) The program described in Appendix 16, wherein in the determination step, if the rotation angle of the first polarization state vector and the rotation angle of the third polarization state vector are in a proportional relationship, it is determined that the length of the first partial period or the length of the interval of the first partial period is appropriate. [Explanation of symbols]

[0160] 1. Optical transmission and reception system 10 Optical transmission signal 20 Optical receiving signal 100 Transmitting device 200 Receiving device 300 Optical Communication Line 1000 Computers 1020 Bus 1040 Processor 1060 Memory 1080 Storage Device 1100 Input / Output Interface 1120 Network Interface 2000 Polarization Status Monitoring Device 2020 Specific Department 2040 Calculation Department 2060 Judgment section 2080 Output section 2100 Changes

Claims

1. an identification means for identifying a first polarization state vector representing the polarization state of the optical reception signal in each of a plurality of first partial periods obtained from the monitoring period, and for identifying a second polarization state vector representing the polarization state of the optical reception signal in each of a plurality of second partial periods obtained from the monitoring period; a calculation means for calculating a rotation angle of the first polarization state vector for each of a plurality of pairs of the first polarization state vector, and for calculating a rotation angle of the second polarization state vector for each of a plurality of pairs of the second polarization state vector; a determination means for determining whether or not a length of the first partial period or a length of an interval of the first partial period is appropriate based on a rotation angle of the first polarization state vector and a rotation angle of the second polarization state vector; and an output means for outputting change rate data representing a rate of change of the polarization state during the monitoring period based on a rotation angle of the first polarization state vector when it is determined that the length of the first partial period or the length of the interval of the first partial period is appropriate, A polarization state monitoring device, wherein the length of the second sub-period is shorter than the length of the first sub-period, or the length of an interval of the second sub-period is shorter than the length of an interval of the first sub-period.

2. 2. The polarization state monitoring device according to claim 1, wherein the determination means determines that the length of the first partial period or the length of the interval of the first partial period is appropriate when a rotation angle of the first polarization state vector and a rotation angle of the second polarization state vector are in a proportional relationship.

3. 3. The polarization state monitoring device according to claim 1, further comprising a change unit that changes a length of the first partial period when the length of the first partial period is not appropriate.

4. the identifying means further identifies, for each of a plurality of third partial periods obtained from the monitoring period, a third polarization state vector representing a polarization state of the optical reception signal in the third partial period; The calculation means further calculates a rotation angle of the third polarization state vector for each of a plurality of pairs of the third polarization state vector, The determination means further determines whether or not a length of the first partial period or a length of an interval of the first partial period is appropriate based on a rotation angle of the first polarization state vector and a rotation angle of the third polarization state vector; the output means outputs the rate of change data when it is determined that a length of the first partial period or a length of an interval of the first partial period is appropriate based on a rotation angle of the first polarization state vector and a rotation angle of the second polarization state vector, and when it is determined that a length of the first partial period or a length of an interval of the first partial period is appropriate based on a rotation angle of the first polarization state vector and a rotation angle of the third polarization state vector, The polarization state monitoring device of claim 3 , wherein the length of the third sub-period is longer than the length of the first sub-period, or the length of an interval of the third sub-period is longer than the length of an interval of the first sub-period.

5. The change means is shortening a length of the first partial period when it is determined that the length of the first partial period is inappropriate based on the rotation angle of the first polarization state vector and the rotation angle of the second polarization state vector, or shortening a length of an interval of the first partial period when it is determined that the length of an interval of the first partial period is inappropriate based on the rotation angle of the first polarization state vector and the rotation angle of the second polarization state vector; 5. The polarization state monitoring device according to claim 4, further comprising: a length of the first partial period being increased when it is determined that the length of the first partial period is inappropriate based on the rotation angle of the first polarization state vector and the rotation angle of the third polarization state vector; or a length of the interval of the first partial period being increased when it is determined that the length of the interval of the first partial period is inappropriate based on the rotation angle of the first polarization state vector and the rotation angle of the third polarization state vector.

6. 5. The polarization state monitoring device according to claim 4, wherein the determination means determines that the length of the first partial period or the length of the interval of the first partial period is appropriate when a rotation angle of the first polarization state vector and a rotation angle of the third polarization state vector are in a proportional relationship.

7. a step of identifying a first polarization state vector representing the polarization state of the optical reception signal in each of a plurality of first partial periods obtained from the monitoring period, and identifying a second polarization state vector representing the polarization state of the optical reception signal in each of a plurality of second partial periods obtained from the monitoring period; a calculation step of calculating a rotation angle of the first polarization state vector for each of a plurality of pairs of the first polarization state vector, and calculating a rotation angle of the second polarization state vector for each of a plurality of pairs of the second polarization state vector; a determining step of determining whether or not a length of the first partial period or a length of an interval of the first partial period is appropriate based on a rotation angle of the first polarization state vector and a rotation angle of the second polarization state vector; and an output step of outputting change rate data representing a rate of change of the polarization state during the monitoring period based on a rotation angle of the first polarization state vector when it is determined that the length of the first partial period or the length of the interval of the first partial period is appropriate, A computer-implemented polarization state monitoring method, wherein the length of the second sub-period is shorter than the length of the first sub-period, or the length of an interval of the second sub-period is shorter than the length of an interval of the first sub-period.

8. 8. The polarization state monitoring method according to claim 7, wherein in the determination step, if a rotation angle of the first polarization state vector and a rotation angle of the second polarization state vector are in a proportional relationship, it is determined that the length of the first partial period or the length of the interval of the first partial period is appropriate.

9. a step of identifying a first polarization state vector representing the polarization state of the optical reception signal in each of a plurality of first partial periods obtained from the monitoring period, and identifying a second polarization state vector representing the polarization state of the optical reception signal in each of a plurality of second partial periods obtained from the monitoring period; a calculation step of calculating a rotation angle of the first polarization state vector for each of a plurality of pairs of the first polarization state vector, and calculating a rotation angle of the second polarization state vector for each of a plurality of pairs of the second polarization state vector; a determining step of determining whether or not a length of the first partial period or a length of an interval of the first partial period is appropriate based on a rotation angle of the first polarization state vector and a rotation angle of the second polarization state vector; an output step of outputting change rate data representing a rate of change of the polarization state during the monitoring period based on a rotation angle of the first polarization state vector when it is determined that the length of the first partial period or the length of the interval of the first partial period is appropriate; The program, wherein the length of the second sub-period is shorter than the length of the first sub-period, or the length of an interval of the second sub-period is shorter than the length of an interval of the first sub-period.

10. The program according to claim 9, wherein in the determination step, when a rotation angle of the first polarization state vector and a rotation angle of the second polarization state vector are in a proportional relationship, it is determined that the length of the first partial period or the length of the interval of the first partial period is appropriate.

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